Devices for carrying out rotary movements under the action of magnetic forces



March 22, 1966 F KARSTENSEN 3,241,924

DEVICES FOR CARRYING OUT ROTARY MOVEMENTS UNDER THE ACTION 0E' MAGNETIC FORCES Filed May 23, 1965 2 Sheets-Sheet 1 \\\\\\\A\\\x\\\\\\\\w 17 1g FIG A b FIGB INVENTOR.

FRI THJOF KA RS TE NSE N AGENT F. KARSTENSEN March 22, 1966 DEVICES FOR CARRYING OUT ROTARY MOVEMENTS UNDER THE ACTION OF MAGNETIC FORCES 2 SheebS-Sheel'. 2

Filed May 25, 1965 INVENTOR.

F Rl THJOF K ARS TE NSEN 'stituent, for example, gallium arsenide. .tive rotation of semi-'conducting rod section must be United States Patent() 3,241,924 DEVICESFGR CARRYING OUT ROTARY MOVE- `MENTS UNDER V'II-IE ACTION OF MAGNETIC FORCES iFrithjof .Karstensem Harksheide, Bezirk Hamburg, Germany, assignr to North American yPhilips Company,

Inc., New York, NY., acorporation of Delaware Filed May 23, 1963, Ser. No. 282,801 Claims priority, Vapplication Germany, Feb. 5, 1960,

7 Claims. (Cl. 23-273) conductor rod may be .Xed and the other end rotated;

each end of the rod may be rotated in opposite directions,

orthe rod portions may be rotated in the same direction at dilferent speeds.

Among the advantages of the relative Vrotation of the rod sections in crystal growing are: improved thermal Y symmetry, and uniform distribution ofthe material constituents in the finished crystal.` These two advantages are particularly important for III/ V semi-conductor compounds of high specific gravity and having a volatile con- However, relacarried out under adverse conditions in a highly reliable manner since the surface tension Iof the molten zone is easily disturbed. For example, the surface tension in the molten zone of III/V compounds such as gallium arsenide, which has a `high density grams per cubic centimeter), can be overcome by unsymmetrical thermal conditions alone and certainly by vibrations or chatter set up in a bearing during rotation or by .allowing the rod sections to imperceptably shift laterally relative to one another.

Another consideration must also be taken into account in providing apparatus for rotatively suspending gallium arsenide semi-conductor crystals during zone-melting treatment due to the volatile nature of gallium arsenide at molten temperature, i.e. arsenic evaporates and separates from the melt at said temperature. It is important therefore to conduct gallium arsenide crystal growth in a controlled atmosphere and thus provide an equilibrium atmosphere at the required temperature and pressure. Since stirring also provides an advantage in this regard it is imperative to provide bearings for the rotatable holder connected with the semi-conductor which are not adversely afectedby the corrosive arsenic'vapor or are shielded from contact with said vapor to avoid bearing vibration, chatter or lateral movement of a bearing supporting the rotating portion of the lsemi-conductor rod.

Heretofore, attempts to overcome the problems outlined above consisted of passing a shaft through a wall of the envelope containing the material to be treated and sealingthis passage while allowing the shaft to rotate therein. In view of the temperature to which the seal is subjected (600 C.) andthe limitation that it cannot Vhave an adverse effect on the semi-conductor material,

graphite is extensively used. However, where arsenic vapors are generated the graphite seal is not as reliable as required. i

conductor materialin which the bearing Vpiece of FIG. 2

prior art.

fice

Attempts have been also made to overcome the above noted problems bythe use of magnets which both suspend the semi-conductorl within an envelope and at the ksame timel causerelative rotation between the rod portions separated by thefmolten zone. While successful, these magnetic systems are quite complex as the magnetic lield must be highly stabilized to prevent even the vslighest movement'which is sufficient to rupture the molten zone. Accordingly an object of this invention, is t-o provide a simple, inexpensive `and highly reliable apparatus to overcome these problems, av presently preferred embodiment of which is illustrated'in the accompanying drawing.

ReferringY to the drawing:

FIG. vl illustrates an arrangement according to the y1 `IG.'2 shows aybearing piece according to an embodiment -of the invention wherein the semi-conductor rod is suspended and driven from above.

FIG. 3 shows a bearing piece according to the invention wherein the semi-conductor rod is held and driven from its lowermost end.

FIGS. 4a and 4b are diagrammatic representations visually explaining the operation of the device according to thepinvention.

FIG. 5 is a View of an apparatus for treating semiis utilized. A

FIG. 6 is aview similar to FIG. 5 wherein the bearing piece according to FIG. 3 is utilized.

zFIG.' 7 is a View of an alternative arrangement for connectingthe bearing shaft with the upper ball race of FIG. 2.

FIG. 8 is a View of an alternative arrangement for connecting the bearing shaft and semi-conductor rod.

axially. Rotation of one rod section may be imparted by magnetic agency in known manner (not shown).

As seen in FIGS. 2 and 5 a rod 2 of semi-conductor material is held in a vertical position between quartz glass holders or clamps 22, 22 within an envelope 5 of quartz glass. The clamp 22 is connected with rotatable shaft V9 which passes Vthrough capillary tube 8 of quartz glass. The tube 8 and the lower ball bearing race 10 are supported within the envelope 5 by means of a quartz glass holder or attachment piece 23.` The lower race 10 may be detachably secured with the piece 23 in any suit able manner. The upper bearing race 11 is secured to the shaft 9 at 12. andtherefore rotates with the shaft ,9 by virtue of the magnets 31, 33 arranged as shown in FIG. 5 or in any other suitable arrangement. An alternative detachable connection between the shaft 9 and upper race 11 is illustrated in FIG. 7 and will be fully described in connection therewith. The upper and lower bearing races 10 and 11 are separated by glass spheres 13 held in a quartz guide ring 14. All the parts of the bearing piece including shaft 9 are preferably madeof quartz. It

will be apparent also that the skirt portion 7 of1attach- `ment piece 23 is accurately ground as is the adjacent and associated clamp 22.

The bearing` piece `10-14 is made for quick and easy dismounting for cleaning purpose when necessary. It

`has been vfound that Ilubrication is unnecessary for a bearingas above described- 'es ,indicated .in FIG. ,fla lwhen the center of gravity v17 of the system acts on the axis of shaft 9 the bearing forces 15, 16 are uniform. If the application of gravity 17 is shifted from this location as indicated in FIG. 4b the forces acting on the bearing are not evenly distributed; nevertheless, the shaft 9 is held firmly by the bearing in its original or aligned position by virtue of the bearing 10-14 and the liquid zone 1 is not disturbed. In this connection and having reference to FIG. 5 it is noted that the ground surface of the skirt 7 of attachment piece 23 and abutting portion of envelope 8 supporting the shaft 9 provide sufficient friction under such conditions to prevent displacement of the shaft 9 or attachment piece 23 relative to the envelope 5.

It should be noted that the glass bearing 10-14 can be accurately manufactured in known manner. Thus, the spheres 13 can be formed from quartz drops and polished A.between glass plates. The apertures or bore through the bearing races and the ring guide can be accurately made by `supersonic drills and polished by known techniques also. The drive for rod 9, and hence the upper portion 2 of the semi-conductor rod 2, 2, is provided by magnets 31 attached to the upper end of shaft 9 and magnets 33 driven by a motor 39 as indicated in the drawing. Of course, any suitable arrangement other than that illustrated may be utilized.

As seen in FIGS. 5 and 6 the apparatus is suitably located between upstanding resistance type electric heaters which heat the entire envelope to the required temperature. The alternative arrangement previously mentioned is illustrated in FIGS. 3 and 6 wherein the rod 2, 2 of semiconducting material is held between suitable clamps 22, 22" and supported in a point bearing located below the rod 2, 2. In this arrangement the shaft to be rotated is designated 9 and is operatively associated with any suitable magnetic arrangement such as indicated in FIG. 6 which is similar to that illustrated in FIG. 5.

The shaft 9 projects beyond the capillary sleeve 8 within the bulbous attachment piece 18 and the accurately ground point 19 of this shaft abuts a planar supporting surface 20 of soft material, such as copper, into which the point 19 can penetrate a small distance to prevent lateral movement thereof. As disclosed above in connection with FIG. 5, the bulb 18 is ground and accurately positioned within the envelope 5 by the converging portion of envelope 5 adjacent the diverging portion of bulb 18.

It will be readily apparent from the foregoing that the bearing pieces seen in FIGS. 2 and 3 and the semi-conducting rod are readily assembled and placed with the envelope 5 which is then sealed in known manner and evacuated or any desirable atmosphere created therein. It will also be apparent that both bearing pieces may be utilized together in a single envelope if desired.

In the operation of the embodiment shown in FIG- URE 5, one of the semi-conductive rods 2, 2 separated by the liquid zone 1 is rotatably arranged while the other is held against rotation. The semiconductive rod 2 is secured to rotatable shaft 9 by means of a clamping device 22 known per se. The supporting rod 9 is passed through a capillary S which is held by a tubular quartz plug 23 having a grounded piece 7. A lower bearing shell 10 is secured on the quartz plug 23 likewise by means of ground abutting surfaces. Between bearing race 10 and upper bearing race 11, balls 13, are maintained spaced apart in the usual manner by means of a guide ring 14.

l the quartz tube 5 in a tting manner.

supporting arm 3S on a shaft 37, for example of an electric motor 39. When the shaft 37 of the motor 39 rotates, the magnet 33 moves along a circular path around the supporting rod 9, magnet 31 is thus taken along by magnet 33, so that the supporting rod 9 is rotated.

The quartz plug 23 is placed with its ground skirt 7 in As in FIG. 1 the quartz tube contains another supporting shaft 3 to which the lower end 2 of semi-conductive rod, separated from upper end 2 by the liquid zone 1 is secured by means of clamping device 22. The high frequency coil 21 is movable in any suitable manner relative to quartz tube 5.

The operation of the embodiment of FIG. 6 will be apparent from the foregoing.

Referring now to FIGS. 2 and 7 it will be seen that the upper race 11 of the ball bearing may be connected to the quartz shaft 9 by a suitable glass Weldment 12 or by the use of a quartz glass sleeve 50 as seen in FIG. 7. The sleeve 50 may be iixedly connected to the rod and removably connected to the upper race by means of flanges 51 which are accurately ground to define a plane perpendicular with the longitudinal axis of the shaft 9. The ground surface of the liange 51 bears on the upper race 11 which is also roughened to provide a driving connec- --tion for shaft 9.

It will be seen from FIG. 8 that, in addition to the known clamp 22, 22 illustrated in FIGS. 5 and 6 for holding the semi-conducting rod, the `shafts 9, 9 may be provided with a bore 60 for receiving one end of the rod 2 which is pinned in place through the horizontal bores 61.

The foregoing presently preferred embodiments of the invention are given by way of illustration and example. Many changes in the embodiments shown are within the skill of the art and such are contemplated Within in the scope of the subjoined claims.

What is claimed is:

1. Apparatus for treating semi-conductor material comprising: an envelope member having a first diameter and a second diameter interconnected by a converging wall section, a bearing piece, a holder, said holder having a concentric capillary tube therein and a tapered portion for fitting within said converging wall portion, a shaft concentric with and extending axially of said capillary tube, a ball bearing having one race supported on said holder and the other race secured to said shaft, magnetic means for rotating said shaft, and means to secure a semi-conductor rod on said shaft at one end and a fixed support secured to said envelope at the other end of said semi-conductor rod; said holder dividing said envelope into first and second discrete compartments, one of which contains said semi-conductor rod.

2. Apparatus for treating semi-conductor material comprising: `an envelope member having aconverging wall section, a bearing piece including a holder having a tapered skirt portion for supporting said bearing piece at said converging wall portion, a capillary tube concentric with and extending axially of said holder, a shaft within said capillary tube, a ball bearing having one race supported on said holder, a skirt member connected with said shaft, said skirt member having a flange frictionally connecting said shaft with the other race of said bearing, magnetic means to rotate said shaft and means to secure a semi-conductor rod on said shaft -at the end remote from said skirt and the other end of said rod to a second holder means within said envelope; said holder dividing said envelope into first and second compartments', one of which contains said semi-conductor rod.

3. Apparatus according to claim 2 wherein said means for securing said semi-conducting rod to said shaft comprises a central bore in said shaft receiving one' end of said rod, said rod and said shaft being provided with a horizontal bore adapted to receive a pin securing said ro within the bore of said shaft.

4. Apparatus for treating semi-conductor material comprising: a glass envelope member having a converging wall section, a glass bearing holder having a concentric capillary tube therein, said holder having a tapered skirt portion engaging said wall section, a lower glass bearing race supported on said holder, a gl-ass shaft concentric within said capillary tube and connected to said lower bearing race, one end of said shaft being removably secured with a glass upper bearing race by means of a glass thimble having a ange frictionally engaging said upper bearing race, and glass ball bearing means intermediate said races; magnetic means for rotating said shaft, and means for connecting a semi-conductor with said shaft at one end, and a xed holder connected to the other end of said rod and secured in said envelope; said holder dividing said envelope into first and second compartments, one of which contains said semi-conductor rod.

5. Apparatus for zone melting semi-conductor rod material comprising a closed tubular envelope member, upper and lower shaft members for supporting a semiconductor rod therebetween and associated bearing means for each said shaft member; said upper bearing means comprising a capillary tube concentrically surrounding a portion of said upper shaft, a holder supported within said envelope and supporting said capillary tube, a xed bearing shell supported at the upper end of said holder, a rotatable bearing shell coaXially spaced from said xed bearing shell and a ball bearing race intermediate said xed and rotatable shells, said rotatable bearing shell being detachably connected with the upper end of said upper shaft member, said lower bearing means comprising a second capillary tube concentrically surrounding a portion of said lower shaft, a second holder supported within said envelope and supporting said second capillary tube, one end of said lower shaft having a pointed bearing and operatively associated with a supporting surface of said second holder.

`6. Apparatus for zone melting semi-conductor materials comprising: an envelope member having a rst diameter and a second diameter interconnected by a converging wall portion, a holder member having a concentric capillary tube therein and a tapered wall portion for fitting within said converging wall portion, said holder dividing the space within said envelope into rst and second discrete compartments, a driven shaft in said capillary tube extending from said first compartment into said second compartment, bearing means connected with one end of said shaft, and means for connecting a semiconductor rod to the other end of said shaft; whereby a corrosive gaseous atmosphere in one said compartment is sealed from entry into the other said compartment.

7. Apparatus for zone melting semi-conductor materials according to claim 6 wherein said driven shaft comprises a point bearing shaft having a magnet attached thereto and associated magnetic means for driving said shaft.

References Cited by the Examiner UNITED STATES PATENTS 2,556,854 6/1951 Spears 310-104 XR 2,745,028 5/1956 Ford S10-104 XR 3,009,973 11/1961 Emeis.

3,113,228 12/1963 Tolegian 310-104 XR 3,113,841 12/1963 Reuschel 23-301 XR NORMAN YUDKOFF, Primary Examiner.

G. HINES, Assistant Examiner. 

1. APPARATUS FOR TREATING SEMI-CONDUCTOR MATERIAL COMPRISING: AN ENVELOPE MEMEBER HAVING A FIRST DIAMETER AND A SECOND DIAMETER INTERCONNECTED BY A CONVERGING WALL SECTOIN, A BEARING PIECE, A HOLDER, SAID HOLDER HAVING A CONCENTRIC CAPILLARY TUBE THEREIN AND A TAPERED PORTION FOR FITTING WITHIN SAID CONVERGING WALL PORTION, A SHAFT CONCENTRIC WITH A EXTENDING AXIALLY OF SAID CAPILLARY TUBE, A BALL BEARING HAVING ONE RACE SUPPORTED ON SAID HOLDER AND THE OTHER RACE SUCURED TO SAID SHAFT, MAGNETIC MEANS FOR ROTATING SAID SHAFT, AND MEANS TO SECURE A SEMI-CONDUCTOR ROD ON SAID SHAFT AT ONE END AND A FIXED SUPPORT SECURED TO SAID ENVELOPE AT THE OTHER END OF SAID SEMI-CONDUCTOR ROD; SAID HOLDER DIVIDING SAID ENVELOPE INTO FIRST AND SECOND DISCRETE COMPARTMENTS, ONE OF WHICH CONTAINS SAID SEMI-CONDUCTOR ROD. 